This is in the part of the movie where Walter Burke is giving his,I suppose I'll call them,'trainees' the tests in the Bug House.The first trainee he and his friend are looking at on the monitors is in a trap bathroom.

Before Burke's friend says,"Doesn't look like it tonight,"(or something like that),look at the bathroom mat the trainee runs across as the alarms go off to escape the room.After he says it,look at it,it's moved in a different position about half a foot away from it's original place.